Conversion of Natural Gas Hydrate into CO2 Hydrate – A Win-win Situation

Injection of carbon dioxide into in situ natural gas hydrate sediments will lead to an exchange in which carbon dioxide will primarily occupy the large cavities of structure I under the release of the original methane in these cavities. The exchange can go directly as a solid state exchange or it can be a result of a hydrate formation dissociation sequence. In the latter case new hydrate from injected carbon dioxide will release heat for dissociation of the in situ methane hydrate. In this case the heat transport is fast and the rate controlling mass transport is liquid transport and as such orders of magnitude faster than the slow solid state mechanism. The conversion is discussed in detail in terms of state of the art multi scale modelling and experimental work. The role of entropy changes in driving the exchange process is discussed in detail. Some highlights of results from a recent pilot plant test of the concept in Prudoe Bay Alaska are also discussed. Finally some remaining challenges, and possible strategies, for the future development of hydrate as an energy resource are discussed.